Fix bin-dir remap to work with --experimental_output_paths=strip

Use add_all with the crate root File and a map_each callback instead
of a hardcoded ctx.bin_dir.path string. This lets Bazel's path mapping
rewrite the config portion of the bin-dir prefix (e.g. k8-fastbuild ->
cfg), so the remap flag matches the actual source file path at
execution time.

Author: Tamas Vajk

rust/private/rustc.bzl

@@ -1200,7 +1200,11 @@ def construct_arguments(
             # line.  The ${pwd} remap above only matches absolute paths in
             # debug info, so a second remap without ${pwd} is needed to
             # strip the bin-dir prefix from these compile-time paths.
-            rustc_flags.add("--remap-path-prefix={}/=".format(ctx.bin_dir.path))
+            #
+            # Use add_all with the crate root File and a map_each callback
+            # so Bazel's path mapping (--experimental_output_paths=strip)
+            # can rewrite the config portion of the bin-dir prefix.
+            rustc_flags.add_all([crate_info.root], map_each = _get_bin_dir_remap_prefix)
 
     emit_without_paths = []
     for kind in emit:
@@ -2714,6 +2718,25 @@ def _add_native_link_flags(
                     format_each = "-lstatic=%s",
                 )
 
+def _get_bin_dir_remap_prefix(file):
+    """Derives a --remap-path-prefix flag that strips the bin-dir prefix.
+
+    For a generated file, file.path is "bazel-out/<config>/bin/<pkg>/<name>"
+    and file.short_path is "<pkg>/<name>".  The difference is the bin-dir
+    prefix that needs to be stripped from file!() and similar macros.
+
+    Using the File object with add_all/map_each lets Bazel apply path mapping
+    (--experimental_output_paths=strip) to the config portion of the path.
+
+    Args:
+        file (File): The crate root file (must be a generated file).
+
+    Returns:
+        str: A --remap-path-prefix flag that maps the bin-dir prefix to empty.
+    """
+    prefix = file.path[:len(file.path) - len(file.short_path)]
+    return "--remap-path-prefix={}=".format(prefix)
+
 def _get_dirname(file):
     """A helper function for `_add_native_link_flags`.